The present invention relates to cylinders and, more particularly, to fixture cylinders having proximity switches mounted to the end caps.
As industry moves more and more into automated robotic systems, applications for fixture cylinders become ever increasing. In the automotive industry, fixture cylinders play a large role in moving parts along an automated assembly line. Fixture cylinders may be adapted to move in a number of different directions accomplishing several different tasks. Thus, these movements enable the fixture cylinder to be utilized in a number of different applications along an assembly line. Cylinders having mounting means on their end caps are generally referred to in the industry as fixture cylinders because they are usually mounted to fixtures used on the assembly line or the like for performing operations on the workpieces.
Generally, air cylinders move parts weighing several hundred pounds. Also, air cylinders are preferred over hydraulic cylinders due to their appealing cleanliness characteristics. When line breakage occurs in an air cylinder system, the air supply is simply turned off and no mess or damage occurs; when a line breakage occurs in a hydraulic cylinder system there is a large cleanup project still remaining after the hydraulic fluid supply to the cylinder has been turned off. Although possessing outstanding cleanliness characteristics, prior air cylinders used in automation applications have several disadvantages. Generally, the air cylinders presently used in the field are of a hydraulic cylinder design and thus are very inefficient as air cylinders. With the movement to computer numeric controls, the prior air cylinders require numerous different spacer members to enable a proximity switch to be functionally mounted on the air cylinders. Also, the spacer members add to the overall height, weight, and bulkiness of the cylinders. With the addition of different spacer members onto the air cylinders, for accommodating proximity switches, two identical proximity switches may be utilized on a single air cylinder for controlling the stroke of the air cylinder. Further, the end caps of these cylinders are generally heavy machined parts adding to the overall weight of the air cylinder.
An air cylinder, known in the field as a Fisher cylinder, exists which was originally designed by Fisher Body as an air cylinder having end caps casted from a ductile or steel material. While having good efficiency characteristics, the Fisher cylinder does not meet National Fluid Power Association (NFPA) specifications and thus the Fisher cylinder is not interchangeable in standard equipment utilizing NFPA specification air cylinders. Also, the Fisher cylinder is not readily adaptable for the addition of proximity switches which limits the Fisher cylinder's use in computer numeric control applications.
Accordingly, the present invention overcomes the disadvantages of the above art. The new and improved air cylinder provides the art with an interchangeable air cylinder having end caps formed from a ductile material which are interchangeable with NFPA cylinders. Also, the present invention provides the art with an air cylinder which eliminates the use of spacer members for accommodating the proximity switches. Thus, the present invention enables the air cylinder to utilize two identical proximity switches for sensing the stroke of the piston.
In accordance with the teachings of the preferred embodiment of this invention, a fixture cylinder is provided that permits the use of integrally mounted proximity switches with the same fixed probe lengths on both end caps without requiring the use of spacers. The cylinder includes a body in which a piston assembly is slidably mounted about a longitudinal piston axis in a bore in the body. The piston assembly has a piston head, piston rod and a pair of hubs on opposite sides of the piston head. First and second end caps are provided on opposite ends of the body. Each end cap has a plurality of outer edges and a generally flat mounting surface is provided on one edge thereof for receiving a proximity switch. An aperture perpendicularly extends through each end cap and communicates with the bore in the body of the piston assembly. Two substantially identical proximity switches having generally flat mounting surfaces and fixed probe lengths are employed. Means are provided for securing the proximity switches to the end caps so that the respective mounting surfaces abut and precisely define the distance that the probes extend towards the piston hub in the bore.